The present invention relates to a mercury electrode switch having a tubular glass housing which is closed on all sides and into one end of which are fused at least one pair of electrodes, the glass housing being indented at a distance from the inside ends of the electrodes.
Mercury electrode switches of this type are known. Such switches, without the indented structure, are disclosed in German Patent No. 2,136,428. Such mercury elecrode switches serve to switch electrical currents, with the switching process being initiated by a tilting movement of the switch. If the switch is tilted in such a way that the mass of mercury in the interior of the glass housing contacts the two electrodes, the circuit is closed, i.e. the switch is on. If the switch is tilted in such a way that the mercury flows away from the electrodes and collects at another location, for example at the opposite end of the glass housing, the switch is off and the circuit is opened.
In view of the high mobility of the mercury, only very small angles with respect to the horizontal position are required to initiate the switching process. The difference in the positions of the switch between the minimum tilt at which it attains its "ON" position, on the one hand, and the minimum tilt at which it attains its "OFF" to position, on the other hand, a difference which is measured in angular degrees, is called the switching hysteresis. In the conventional, unrecessed, mercury electrode switches this angle is only a few angular degrees.
In some cases it is desired to increase the switching hysteresis. For such cases it is known to indent the glass housing at a distance from the inside ends of the electrodes. The switch must then be installed in such a manner that its recess comes to lie at the bottom. The recessing considerably increases the switching hysteresis since the mass of mercury must flow over the obstruction formed by the recess to go from the one end of the switch, the end without the electrodes to the other end of the switch equipped with the electrodes. Correspondingly large is the opposite tilt angle which the switch must traverse for the mercury to flow away from the inside ends of the electrodes in order to open the circuit.
The known recessed mercury electrode switches have the drawback that their housing recesses can become effective only if the switch is installed in a certain position. This cannot always be accomplished during installation of the switches in the devices to be switched so that rejects are unavoidable. But even if the switch is installed in the correct position, the instrument equipped with such a switch cannot operate properly if the instrument itself is placed in a position other than the one intended by its designer.
In order to provide position independent, recessed mercury electrode switches it is known to equip the glass housing of the switch with a recess that covers the entire circumference, i.e. an annular constriction. Such mercury electrode switches have not found commercial acceptance since it has happened again and again that the mass of mercury becomes stuck in the constricted portion of the glass housing. This problem occurs with particular frequency if the switch is filled with a protective gas. Mercury electrode switches with such complete circumferential constriction are therefore designed with preference as vacuum switches. But even with such constricted vacuum switches, the mercury cannot be positively prevented from getting stuck in the constricted section.